O o d h e a d p u b L i s h I n g L i m I t e d

7.4
Insect-resist and insect-repellent treatments
Woollen goods are susceptible to attack from the larvae of certain species of
moth and beetle. This can be a particular problem for goods which lie
undisturbed for long periods of time, for example carpets, blankets, upholstery
fabrics, insulation in buildings and museum specimens. There are some 30
species of moths (Lepidoptera), 15 species of beetles (Coleoptera) and numerous
chewing lice (Mallophaga) which have developed the ability to derive nutrition
from keratin. In some cases this ability and a preference for a keratin diet
have resulted in particular moths and beetles becoming major textile pests.
Lewis and Shaw (1987) reviewed the important wool-damaging moths and
beetles, as shown in Table 7.1.
Table 7.1 Significant wool-damaging insect species
Common name
Scientific name
Common or webbing clothes moth
Tineola bisselliella (Hummel)
Case making clothes moth
Tinea pellionella (Linnaeus)
Tinea translucens (Meyrick)
Brown house moth
Hofmannophila pseudospretella (Stainton)
Carpet beetles
Anthrenus flavipes (Le Conte)
Fur beetles
Attagenus pellio (Linnaeus)
Attagenus piceus (Oliver)
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The generally accepted explanation of the mechanism of wool digestion
by keratophagous insects is that larval guts contain an alkaline-reducing
environment together with highly active proteolytic enzymes. The highly
reducing conditions provided from the larval midgut are capable of breaking
down the disulphide crosslinks of the ingested wool, and the proteolytic
enzyme systems then digest the reduced wool almost completely (McPhee,
1971).
Early developments in insect-resist finishes have been reviewed by Lewis
and Shaw (1987), McPhee (1971), Lewis (1992) and Barton (2000a).
Researchers have approached insect resistance in different ways, including
chemical modification of wool, chemical control of insect behaviour,
antimetabolites (disruption of the insect’s metabolic cycle), insect growth
regulators, microbial pathogens and biological control.
Chemical modification of wool to reduce or eliminate insect attack involves
inhibiting enzyme attack and protein digestion by the insect. Insects are
typically attracted by the leftover smell of food stains and body oils on wool
material. Their survival relies on the protein nutrition which the insects
digest from the interior of fibre. Reduction of the cystine linkages in the
fibre and replacement by non-reducible crosslinks has been attempted in
the past (Moncrieff, 1950)
  to resist the enzymatic digestion by insects.
The technique has not been developed and used commercially since the
chemical changes degrade the physical and chemical properties of the treated
wool.
Biological control of many insects can be achieved by use of microbial
pathogens that attack the insect population. Certain types of microbial pathogens
such as bacteria and fungi can be devastating to insect populations; however,
little research has been undertaken into the use of this method to control
insect attack on textiles. Initial studies have indicated that the powerful
proteolytic enzyme systems in keratophagous insects render these systems
ineffective.
Chemical methods of insect control have involved the use of chemicals to
control insect behaviour, ‘antimetabolites’ which disrupt the insect’s metabolic
cycle, and insect growth regulators. Treatments such as juvenile hormones
that prolong the insect’s life in the harmful larval stages are counterproductive.
In order to protect wool from insects during storage or use as an insulation
material, manufacturers have explored the use of diatomaceous earth and
boron compounds to eliminate insects by attacking the protective waxy outer
layer of the insect, resulting in dehydration and death. It was also found that
treatment of wool with cationic surface active agents may cause the death of
the larvae, resulting in insect resistance (Gibb et al., 2005). Unfortunately
cationic agents are incompatible with the usual anionic dyeing systems used
on wool.
To date, industrial control of keratophagous insects has been through use
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Wool finishing and the development of novel finishes
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of pesticides that kill or control the pests. There are two types of pesticides
(digestion-affecting poisons and nerve poisons) used in insect-resistant
finishing. Digestion-affecting poisons interfere with the keratin-digesting
process of the larvae and include chlorinated triphenylmethane, chlorphenylids,
sulcofuron and flucofuron. Nerve poisons are to kill insects by preventing
nerves from functioning, thereby stopping muscle function, such as permethrin,
cyfluthrin and hexahydropyrimidine (
Fig. 7.9).
 Both types of chemical methods
function by entering the larvae’s digestive tract with ingested wool. These
commercial insect resist agents have typically been applied in the dyebath
when the wool is dyed where they penetrate the wool fibre. They are released
in the insect gut when the fibre is totally digested, thereby providing a
degree of specificity as all other animals (including humans) are incapable
of digesting and degrading wool if they ingest it.
Unfortunately application of insect resist agents in the dyebath cannot be
100% effective and some release into the environment is inevitable. All of
the current treatment chemicals are toxic to aquatic life and are distinctly
‘un-green’. Permethrin has been the main insect-resist agent used commercially
since its development in the mid-1970s because of its cost, its safety to
humans, its versatility of application, its suitability for wool and wool/synthetic
blends and its effectiveness against a wide range of insects. Current permethrin-
based commercial insect-resist agents are listed in 
Table 7.2.
 An alternative
7.9
 Chemical structures of insecticide: permethrin, cyfluthrin and
hexahydropyrimidine derivative.
H
3
C
H
3
C
O
O
N
N
O
O
N
H
Cl
Cl
Hexahydropyrimidine derivative
F
CN
Cl
Cl
O
O
O
H
3
C
CH
3
Cyfluthrin
O
O
O
Cl
Cl
H
3
C
Permethrin
H
3
C
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Advances in wool technology
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insect-resistant agent is based on bifenthrin, another synthetic pyrethroid
insecticide. Formulated by Melbourne Aniline & Lye Pty Ltd, bifenthrin is
claimed to be more effective than permethrin because of better exhaustion
onto the wool and this decreases the amount of active ingredient remaining
in the waste effluent.
Currently, the wool textile industry applies insect-resistant agents mainly
to carpet wools. The UK Environmental Agency has set increasingly stringent
restrictions on the level of permethrin and other insect-resist agents permitted
in effluents. Therefore achieving effective insect-resistance in wool carpets
without compromising the environment has been an ongoing priority. Different
approaches have attempted to improve permethrin fixation during application
and to limit release of permethrin into wastewater. It was reported by Barton
(2000a) that a low-temperature dyeing auxiliary, Valsol LTA-N (Asia Pacific
Specialty Chemical Ltd) can improve the pyrethroid exhaustion onto the
wool and thus lower the concentration of the insect-resistant agent required
in the dyebath.
Foam and dry applications have been developed for effluent-free application
of insect-resistant agents. The Wool Research Organisation of New Zealand
(now AgResearch) developed the Lanaguard technology for insect-resistance
treatment using a powder coating method. The dry powder-containing
pyrethroid and polymer carrier is sprinkled onto the carpet pile. During the
curing stage, the polymer carrier melts and adheres to the wool fibre surfaces
to give insect resistance. There is no water involved (Barton, 2000a).
The major suppliers of insect-resistant agents are urgently searching for
green technology or alternative methods that can result in less environmental
impact. In the absence of an alternative ‘safe’ product, pesticide-based
mothproofing finishes have been significantly reduced.
A new insect-resistant agent based on chlorfenapyr (
Fig. 7.10),
 Mystox
MP, has recently been developed by Catomance Technologies, UK, in
conjunction with AgResearch. Mystox MP is claimed to have the dual function
of contact insecticide and stomach poison. It can be used for protecting
wool, wool blends and carpets. It is claimed to have a low environmental
impact on waterways and environmental risk assessments based on toxicity
to aquatic organisms are reported to show that Mystox MP is up to 30 times
Table 7.2 Commercially available insect resist agents for wool
Mothproofing agents
Commercial products
Permethrin (synthetic
Perigen New (Stephenson Thompson)
pyrethroids)
Eulan SPA (Lanxess)
Mystox MP (Catomance)
Crosproof PEM (Eurodye-CTC)
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less toxic than currently used permethrin-based insect resist agents (Wool
Record, 2007). Detailed data are not yet available.
Microencapsulation technology has recently been utilised in insect-resist
finishing for wool carpets in order to reduce the level of insecticide agents
in wastewater. Insect-resist agents were encapsulated in yeast and applied to
wool carpets. It was reported that moth larvae are attracted to yeast as a
source of nutrients. Using these targeted microcapsules, the levels of insecticide
on carpets could be reduced (Nelson, 1991). Thor SARL (Salaise sur Sanne,
France) has developed a method of microencapsulating the synthetic pyrethroid
permethrin (Holme, 2007a).
With increasingly stringent effluent consent levels for toxic pesticides, it
is certain that time is fast running out for the permethrin-based products that
have served the industry for almost half a century. Research and development
into alternative insect-resist technologies is urgently required to ensure that
alternative mothproofing agents are effective on moth and beetle larvae but
have no toxic effects on other species and have minimum impact on the
environment.